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Comcast bridge mode issues

Here's the scenario: Client uses Comcast and has the Comcast Business modem/router (I won't call it the gateway here to avoid confusion) . I put it in bridge mode and configured the public static IP address on the public side of a Sonicwall TZ400 (X1) and set up DHCP for a private subnet and forwarded a port to a test machine inside. When I do that I get nothing, in or out. I suspect that it is the Comcast gateway address. Before putting the comcast router in bridge I did note what they said was the gateway address but it doesn't seem to work.

My question is, is there a way to verify what the comcast gateway address is supposed to be for a specific public IP?. Should the last v4 octet be 1 more or less than the public static address, as I have seen before, or could it be most anything? I hate Comcast and their AI gatekeeper. Can't get through to anyone other than script-readers and only then after three or four tries to get to a human at all. Thanks in advance.

Category: Entry Level Firewalls


  • Hello @NetDel,

    Welcome to SonicWall community.

    Based on the public IP and subnet mask, you can see the usable IP range and the gateway should be one of them.

    For example, if the public IP is and subnet mask is, then the usable range is - So, the gateway is definitely If the subnet mask is anything other, there will be multiple usable addresses and any one of them can be the gateway. Public IP, subnet mask and the gateway details should be provided by Comcast.

    I use this tool for IP subnet calculation and find it very handy.

    I hope this helps!


    Shipra Sahu

    Technical Support Advisor, Premier Services

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